This invention relates to apparatus and methods for delivering medication to the respiratory system of a patient through an invasive or noninvasive pressure-assisted breathing system. More specifically, one aspect of the invention is directed to apparatus and methods for coupling an aerosol generator (nebulizer) with a continuous positive pressure airway (“CPAP”) or bi-level positive airway pressure (“Bi-level”) system. The use of CPAP and Bi-level systems and therapies are conventional forms of non-invasive ventilation treatment for respiratory disorders in adults, e.g. obstructive sleep apnea and respiratory insufficiency, and in children, e.g. abnormal breathing resulting from small or collapsible airways, small lung volumes, muscle weakness, respiratory distress syndrome, persistent obstruction following surgery, etc. Systems that utilize an endotracheal or tracheotomy tube are examples of invasive pressure-assisted breathing systems. As used herein, the term “pressure-assisted breathing system” is intended to include non-invasive systems such as CPAP and Bi-level systems, as well as invasive systems.
Pressure-assisted breathing systems utilize positive pressure during inhalation to increase and maintain lung volumes and to decrease the work of breathing by a patient. The positive pressure effectively dilates the airway and prevents its collapse. The delivery of positive airway pressure is accomplished through the use of a positive air flow source (“flow generator”) that provides oxygen or a gas containing oxygen through a flexible tube connected to a patient interface device such as nasal prongs (cannula), nasopharyngeal tubes or prongs, an endotracheal tube, mask, etc. CPAP devices typically maintain and control continuous positive airway pressure by using a restrictive air outlet device, e.g. a fixed orifice or threshold resistor, or a pressure valve, that modulates the amount of gas leaving the circuit to which the patient interface device is attached. This pressure regulating device may be placed at, before or beyond the patient interface device and defines a primary pressure-generating circuit. During the course of CPAP therapy, the patient may inhale only a fraction of the total flow of gas passing through the primary pressure-generating circuit.
Bi-level systems deliver continuous positive airway pressure but also have the capability to sense when an inspiratory and expiratory effort is being made by the patient. In response to those efforts, Bi-level systems deliver a higher level of inspiratory pressure (IPAP) to keep the airway open and augment inspiratory volumes as a patient breathes in to reduce the work of inhalation, and deliver a lower expiratory pressure (EPAP) as the patient exhales to keep the airway and lungs open during exhalation. Thus, a Bi-level device employs pressure sensors and variable pressure control devices to deliver at least two levels of air pressure that are set to coincide with the patient's inspiratory and expiratory efforts. Bi-level has been found to be useful for a wider range of respiratory disorders than using CPAP alone, particularly in infants and small children.
An aerosol generator or nebulizer has been used to deliver an aerosol of medication through a ventilation device into the respiratory system of a patient. For example, U.S. Pat. No. 6,615,824, issued Sep. 9, 2003, and in co-pending U.S. patent application Ser. No. 10/465,023, filed Jun. 18, 2003, and Ser. No. 10/284,068, filed Oct. 30, 2002 describe apparatus and methods for connecting a nebulizer to a ventilator circuit to emit a medicament directly into the flow of gas being delivered to a patient's respiratory system.
Use of a nebulizer in connection with a pressure-assisted breathing system having a positive pressure-generating circuit with continuous flow through the circuit, such as many CPAP and Bi-level systems, presents certain challenges. Hence, this invention is related generally to addressing such challenges.